1. Field of the Invention
This invention relates to a control device for driver member under the control of which the intermittently moving driver member (cam) and its follower member (cam follower) act to effect a predetermined operation.
2. Description of the Prior Art
Generally, mechanical apparatuses often use a cam rotatable on an axis and a cam follower following the movement of the cam when it is desired to repeat such a cycle of operation that a certain member is displaced from a certain first position to a second position at a certain period of time and retained at the second position for a predetermined time, whereafter the member is returned to the first position. Such a system utilizes the ramp surface of the cam to provide the displacement and this leads to an advantage that the displacement between the first and the second position can take place smoothly without any shock involved, as well as an advantage that the drive source may be relatively small even when a great force is required for the displacement.
However, in such conventional use of the cam, the cam is caused to make one complete rotation at a predetermined angular velocity and during that time, all operations--for instance, displacement, retention and displacement (return)--are accomplished. The relation between the angle of rotation .alpha. of the cam and the time t and the displacement .chi. of the cam follower is illustrated in FIG. 12 of the accompanying drawings. With such conventional use of the cam, the cam is rotated always at a predetermined angular velocity and accordingly, the angle .alpha. and the time t are in proportional relationship.
Usually in designing a camming mechanism, the retention time t.sub.2 is first determined and then the displacement times t.sub.1 and t.sub.3 are added before and after the retention time. Then, the time T required for one complete rotation of the cam, namely, the rotational velocity of the cam, is determined so that these three t.sub.1, t.sub.2 and t.sub.3 may be satisfied in one complete rotation. In this case, it will be optimum if T can be set so that t.sub.1 +t.sub.2 +t.sub.3 =T. Actually, however, this is not always possible in relation to other parts but there may sometimes occur a relation that t.sub.1 +t.sub.2 +t.sub.3 &lt;T which may result in wasteful rotation of the cam, or in some cases it may be unavoidable to adopt a relation that t.sub.1 +t.sub.2 +t.sub.3 &gt;T. In the latter case, the displacement times t.sub.1 and t.sub.2 must be reduced to secure the absolutely necessary retention time t.sub.2 and this will mean the displacements accompanied by shocks and the loss of the advantage of using the cam.
Also, if the retention time t.sub.2 is long, the time T required for one complete rotation of the cam must be increased and in this connection, a wide-range speed reduction mechanism must be provided in the drive path from a drive source such as motor or the like to the cam, which leads to complex construction of the machine or necessity for a greater space.
Further, if the absolute values of the displacement times t.sub.1 and t.sub.3 are equal to keep smoothness of displacements but the retention time is longer and accordingly its ratio to one complete rotation T on the angles .alpha..sub.1 and .alpha..sub.3 are smaller, the angle of the ramp surface in the cam for displacement will be steeper so that the pressure with which the cam follower is urged against the ramp surface of the cam will be greater. This will promote the abrasion of the cam and cam follower which will also give rise to the problem of poor durability particularly when fine or subtle movements are required. In addition, the cam and cam follower must be structurally sturdy. Further, the torque exerted on the clutch will also be greater and this means that the clutch used must be of a great capacity.
Furthermore, since the mechanism now under discussion is based on the presupposition that the cam is caused to make one complete rotation at a predetermined angular velocity to effect the operation or that T is constant, the retention time t.sub.2 is determined as invariable by the retention angle .alpha..sub.2 resulting from the cam geometry. Therefore, if it was desired to use the mechanism for the same operation but with the retention time t being variable, the cam usually was unusable. Also, if it was attempted to secure the retention time t.sub.2 for the same cam with the angular velocity of the cam being varied by a speed reduction device or the like, the displacement times t.sub.1 and t.sub.2 would be varied together and this would also be inconvenient.